1. Joined
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    19 Jul '08 16:342 edits
    I was talking with someone the other day about alternative energy sources and they mentioned that nuclear fusion is probably one of the few answers in terms of providing energy for the masses in a "safe" way. It has been done, however, it takes far more energy to produce such a reaction than it produces from the reaction and therefore, is not cost beneficial as of yet.

    My question is for all you science buffs out there. Do any of you think it will one day replace nuclear fission, which has problems such as radioactive waste and potential melt downs etc. and/or are there any other potential energy sources out there that shows potential?
  2. At the Revolution
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    19 Jul '08 19:11
    Originally posted by whodey
    I was talking with someone the other day about alternative energy sources and they mentioned that nuclear fusion is probably one of the few answers in terms of providing energy for the masses in a "safe" way. It has been done, however, it takes far more energy to produce such a reaction than it produces from the reaction and therefore, is not cost beneficial ...[text shortened]... downs etc. and/or are there any other potential energy sources out there that shows potential?
    Fusion is, in theory, no less dangerous. Some examples:

    The Hydrogen bomb is a fusion bomb. Most nuclear weapons nowadays, come to think of it, use fusion.

    Fusion is what drives the Sun.

    It needs immense heat and very flammable elements (such as hydrogen). That, of course, does not sound good.

    No releases, maybe, but the explosions if a fusion reactor failed would range from inconvenient to apocalyptic, depending on the size of the reactor. A small bomb was enough to wipe out an island, for comparison.
  3. Joined
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    19 Jul '08 19:52
    In actual fact fusion power plants are very safe, much safer then fission plants.

    It is not possible for a fusion explosion to result from a malfunction of a fusion power plant. This is because fusion power plants (at least the ones we have at the moment) work using a super heated plasma. The fusion fuel is in the plasma, which needs to be very hot so that the particles have sufficient energy to overcome the repulsive electromagnetic forces and get close enough to each other for the strong nuclear force to take over and allow fusion. The fuel needs to be fed into the reactor continuously, only a TINY amount of fuel is in the reactor at any one time. So even a catastrophic failure can not result in a fusion explosion. If containment is breached and the plasma released the density is no longer sufficient for fusion. If the flow of plasma components is disrupted in any way the reaction stops, it cannot spiral out of control in a chain reaction.

    This is different from a FISSION reactor, where all the fuel is in the reactor at once. If a fission reactor runs out of control there can be a chain reaction which results in a nuclear explosion and/or meltdown. If a FUSION reactor runs out of control all the reactor fuel is exhausted before more is injected and it simply stops, no explosion.

    Infact, even if bombs are placed inside a nuclear FUSION plant in strategic places they will never cause a nuclear explosion because disrupting/interrupting the process in any way just makes it stop. Fusion reactors are very safe indeed. They do produce some radioactive waste, but with half-lives much shorter the fission.
  4. SubscriberAThousandYoung
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    19 Jul '08 21:221 edit
    Originally posted by scherzo
    It needs immense heat and very flammable elements (such as hydrogen). That, of course, does not sound good.
    Fusion can be done with any element lighter than iron. You could use helium in theory, and it's not flammable. Hydrogen is the easiest one to fuse though I think.
  5. Joined
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    20 Jul '08 01:381 edit
    Originally posted by MattP
    In actual fact fusion power plants are very safe, much safer then fission plants.

    It is not possible for a fusion explosion to result from a malfunction of a fusion power plant. This is because fusion power plants (at least the ones we have at the moment) work using a super heated plasma. The fusion fuel is in the plasma, which needs to be very hot so tha ...[text shortened]... e indeed. They do produce some radioactive waste, but with half-lives much shorter the fission.
    Thanks for that info. I would also assume that there is no radioacitve waste to worry about with fusion plants as well?

    You say that there are fusion plants in existence today. If so, where? Also, if they exist, are they cost effective to run and if they are, why are not more produced? If they are not cost effective, why then are they in existence today?
  6. Subscribersonhouse
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    20 Jul '08 02:052 edits
    Originally posted by scherzo
    Fusion is, in theory, no less dangerous. Some examples:

    The Hydrogen bomb is a fusion bomb. Most nuclear weapons nowadays, come to think of it, use fusion.

    Fusion is what drives the Sun.

    It needs immense heat and very flammable elements (such as hydrogen). That, of course, does not sound good.

    No releases, maybe, but the explosions if a fusion re ...[text shortened]... nding on the size of the reactor. A small bomb was enough to wipe out an island, for comparison.
    You are thinking in terms of chemistry about the threat of hydrogen.
    When you fuse H2 or deuterium you use so little as to be not much of a threat, one pound of hydrogen would power a plant for a long time so you don't have to store even as much hydrogen as a hydrogen fill station for cars. The total amount of energy in one Kg of matter, if it could be used as such, would power a 100 watt light bulb for thirty million years or 30 MILLION watts for 100 years. Now fusion is only about 1 percent as potent as that but it still means one Kg of H2 could produce 30 megawatts for a year. So there is no threat at all of storing Hydrogen. Besides, there are metal hydrides that adsorb h2 on surfaces where it is only given off as you need it, that technology is being developed for hydrogen powered cars. So if we ever get a fusion plant working, worry about exploding hydrogen won't be one of them.
  7. Joined
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    20 Jul '08 06:46
    Originally posted by sonhouse
    You are thinking in terms of chemistry about the threat of hydrogen.
    When you fuse H2 or deuterium you use so little as to be not much of a threat, one pound of hydrogen would power a plant for a long time so you don't have to store even as much hydrogen as a hydrogen fill station for cars. The total amount of energy in one Kg of matter, if it could be use ...[text shortened]... So if we ever get a fusion plant working, worry about exploding hydrogen won't be one of them.
    Make the calculations:

    Use one kilogram of Hydrogene. What kind of isotope will you use?
    Fuse it into Helium. What kind of isotope will you get?
    How much Helium will you get?
    In mass, what will be the difference? This is the loss of mass.
    Using the E=mc^2 formula, convert the loss of mass into energy, how much energy will this give, if the efficiency is 100%
    But we know that efficiency is not 100%, what will the efficiency be in reality at the power plant?
    How much energy will you get with the real efficiency in mind?
    How long will a 100 Watt light bulb be burning on one kilogram of Hydrogene, realistically?
  8. Subscribersonhouse
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    20 Jul '08 07:01
    Originally posted by FabianFnas
    Make the calculations:

    Use one kilogram of Hydrogene. What kind of isotope will you use?
    Fuse it into Helium. What kind of isotope will you get?
    How much Helium will you get?
    In mass, what will be the difference? This is the loss of mass.
    Using the E=mc^2 formula, convert the loss of mass into energy, how much energy will this give, if the efficien ...[text shortened]... nd?
    How long will a 100 Watt light bulb be burning on one kilogram of Hydrogene, realistically?
    It shouldn't be too far off what I said. 1 Kg converted 100% will power a 100 watt bulb for 30 million years. The figure I used was based on thermonuclear bomb, which may be a bad assumption but it converts about 1 % of the mass available to energy. So if that holds then it should run a 1 watt bulb for 30 million years or a 30 megawatt load for 1 year.
    Of course it takes energy to get fusion going and the ITER is supposed to produce more than it takes to run by about 5 to 1 so if that is the case, then 25 megawatts for one year. Heck, even if it took 10 Kg, that is a lot of power for not much mass! The ITER is not commercially viable even if it achieves that 5 to 1 ratio, a real reactor needs more like 20 to 1 to be commercially useful.
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    20 Jul '08 08:08
    Originally posted by sonhouse
    It shouldn't be too far off what I said. 1 Kg converted 100% will power a 100 watt bulb for 30 million years. The figure I used was based on thermonuclear bomb, which may be a bad assumption but it converts about 1 % of the mass available to energy. So if that holds then it should run a 1 watt bulb for 30 million years or a 30 megawatt load for 1 year.
    Of ...[text shortened]... t achieves that 5 to 1 ratio, a real reactor needs more like 20 to 1 to be commercially useful.
    When we talk about 100% efficiency, do we use E=mc^2 right off? Converting 1 kg hydrogen into energy? In fusion plants this is not the case, not at all, far from it.

    Let's compare with a H-bomb for a while. How efficient is this? Does it convert 100% of it into energy? I say no, not at all. I would think the efficiency is lower than 1%. We are not talking of anti-matter that converts every anti-hydrogne atom into energy. The rest product of H fusion is Helium. The difference in mass, if you compare mass in with mass out, is minute.

    But even if we let us be impressed by the power of an H-bombs efficiency, we cannot use the energy output to convert into electiricy. Almost 100% is converted to heat, ultimately it's actually 100% in the end.

    I suspect you haven't done any calculations as I described. You're an engineer, you're not a theoretic, you know how hard it is to make a process efficient, you always have losses everywhere, and these losses you have to chill out in some ways.

    So, please, do the calculations. Use the scheme I proposed, and see what you come out with. And 100% efficiency?, forget that.
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    20 Jul '08 08:55
    Originally posted by FabianFnas
    When we talk about 100% efficiency, do we use E=mc^2 right off? Converting 1 kg hydrogen into energy? In fusion plants this is not the case, not at all, far from it.

    Let's compare with a H-bomb for a while. How efficient is this? Does it convert 100% of it into energy? I say no, not at all. I would think the efficiency is lower than 1%. We are not talk ...[text shortened]... e the scheme I proposed, and see what you come out with. And 100% efficiency?, forget that.
    I am not sure of the efficiency of the theoretical maximum efficiency of a fusion plant.

    It is worth noting that energy converting to heat is not necessarily waste, this is the first steep in the process. Electricity is not generated directly from the fusion, instead it is heat which is harnessed from the reactor. The heat is transferred away from the reactor and used to make steam to drive turbines.

    Also, Sonhouse's figure for powering a light bulb is believable. I havn't dont the calculation as you described, but I do know that 1kg of fusion fuel (appropriate mix of dueterium and tritium) can output the the same amount of energy as MILLIONS of kg of fossil fuel. This is not an exaggeration, I forget the exact number of millions, but it is that order of magnitude!
  11. Joined
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    20 Jul '08 09:062 edits
    Originally posted by whodey
    Thanks for that info. I would also assume that there is no radioacitve waste to worry about with fusion plants as well?

    You say that there are fusion plants in existence today. If so, where? Also, if they exist, are they cost effective to run and if they are, why are not more produced? If they are not cost effective, why then are they in existence today?
    Some radioactive helium is produced, and the metals in the case of the reactor also become radioactive. The half-life of these materials is much much smaller then things produced by fission. I forget the exact numbers, but FISSION products have half-lifes of hundreds of thousands of years; but FUSION products have half-lifes of hundreds (perhaps thousands???) of years, anyway, much much shorter.

    Radioactive metal in the reactor case can be diluted down with non-radioactive metal to bring it down to acceptable levels and then reused with no ill effects.

    There are fusion plants in existence today. If you look up JET (Joint European Torus) you will find all about the current generation. The current generation can only fuse for a few seconds at a time, it takes a very large amount of energy (it has its own normal power plant on-site to power it) to get it started, then it only fuses for around a second. During the fusion stage it produces positive energy (more out the going in), but because it only runs for a second this output is less then the amount needed to get it started. So no net energy is output.

    However, the JET reactor was required to test some things out. It was always meant as a research reactor, never a commercial one.

    ITER is the new fusion reactor being built in France. It will use knowledge gained from JET and will be able to sustain fusion at a larger rate for hundreds of seconds.

    The plan at the moment is for the generation of fusion plants that follows ITER to be commercial plants that can run continuously.
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    20 Jul '08 09:29
    This is an interesting discussion, disregarded if I'm right or if i'm wrong.

    I think that you cannot compare the nuclear fusion reaction in a H-bomb, which is higly chatotic and generate nothing more than heat in a very short instant of time, and a highly controlled reaction in a fusion plant to generate electric power.

    The most interesting fusion reaction is this:
    D + T -> He-4 + n + 5.2x 10^-13 J
    How many D+T is there in one kilograms of input? Please, help me in this calculation.
    This amount multiplied with 5.2x 10^-13 Joule gives the total energy of one kilogram of fuel in 100% efficency. How many kilowatthour is this?

    This far we can all be agreed, right?, but what is debateable thereafter is about the efficiency of the process to generate electrical power.
  13. Joined
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    20 Jul '08 10:22
    Originally posted by FabianFnas
    This is an interesting discussion, disregarded if I'm right or if i'm wrong.

    I think that you cannot compare the nuclear fusion reaction in a H-bomb, which is higly chatotic and generate nothing more than heat in a very short instant of time, and a highly controlled reaction in a fusion plant to generate electric power.

    The most interesting fusion r ...[text shortened]... is debateable thereafter is about the efficiency of the process to generate electrical power.
    I havn't checked your formula, but assuming it is correct (I dont know off the top of my head), lets put some numbers in it to get an estimate.

    Deuterium is 1 proton and 1 neutron, so has a mass of 2a.m.u.

    Tritium is 1 proton and 2 neutrons so has a mass of 3a.m.u.

    The equation has one deuterium and one tritium joining together. So for each reaction we require 5a.m.u of matter. (a.m.u is atomic mass units by the way. 1 a.m.u = 1.6*10^-27kg).

    So for each reaction we need 5*1.6*10^-27 = 8*10^-27kg of fuel.

    So with one kg of fuel we can have 1/(8*10^-27) = 1.25*10^26 reactions.

    Each reaction puts out 5.2*10^-13J, so from one kg of fuel we get:

    5.2*10^-13 * 1.25*10^26 = 6.5*10^13J

    So now lets convert this into kilowatthours (kWh) as requested.

    1 kWh is 1000J of energy every second for an hour.

    In an hour there are 60*60 = 3600 seconds.

    So for 1kW/h we need 1000*3600 = 3.6*10^6J

    So from our 1kg of fuel we get 6.5*10^13 / 3.6*10^6 = 18.1*10^6kWh!

    Perhaps not enough to get a light bulb running for millions of years (works out at about 20,000 years for a 100W bulb), but still a vast amount of energy! AND all from just 1kg of fusion fuel!

    Also, to address the start of your post. we can compare neclear fusion reaction in a H-bomb with that in a reactor. It is the exact same process, but the reactor has it happening a small amount at once over a long time whereas the bomb does it all at once in a chain reaction. The energy output is the same as long as the same amount of material has been fused. Also, you keep talking about "nothing more then heat" is generated. This is the same as in a coal powerplant, you burn the fuel to get HEAT. The heat is then transferred into electricity, usually by using pressurised gas in a turbine. This is what happens in a fusion plant also, we dont get electricity straight from the reaction.

    However, it turns out that the higher the temperature of a reactor the more efficient the heat transfer stage of the process is. Fusion reactors have temperatures of literally 100million K, so are far FAR hotter then normal power plants. So I imagine that they are more efficient. But as you correctly point out they will not be anywhere near 100%!

    I hope this was helpful 🙂 You may want to check my calculations because I was in a rush hehe.
  14. Standard memberflexmore
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    20 Jul '08 10:434 edits
    Originally posted by MattP
    ... we can compare neclear fusion reaction in a H-bomb with that in a reactor. It is the exact same process, but the reactor has it happening a small amount at once over a long time whereas the bomb does it all at once in a chain reaction. ....
    unfortunately this is not true, a Hbomb is very different from our hypothetical clean fusion reactor ... a H bomb is a sucker of neutrons ... it wants neutrons, it must be bombarded by masses of neutrons or the reaction will die, that is why they start with "heavy water" - hydrogen with as many neutrons as the hydrogen can carry ...

    a common myth is that uranium is used to start the fusion reaction and then the fusion takes over ... it is wrong ... the fusion reaction needs the fission reaction every step of the way.

    h bombs suck in neutrons like a vacuum cleaner on steroids ...

    the only way known to get loads of floating neutrons is with fission reactions ... lots of them .. loads of them ... big h bombs use a lot of uranium, huge amounts of uranium, and make a dirty great mess - they must be about the messiest thing imaginable.
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    20 Jul '08 12:111 edit
    Originally posted by MattP
    I havn't checked your formula, but assuming it is correct (I dont know off the top of my head), lets put some numbers in it to get an estimate.

    Deuterium is 1 proton and 1 neutron, so has a mass of 2a.m.u.

    Tritium is 1 proton and 2 neutrons so has a mass of 3a.m.u.

    The equation has one deuterium and one tritium joining together. So for each reaction hope this was helpful 🙂 You may want to check my calculations because I was in a rush hehe.
    Then I owe sonhous an apology, he was more right than I thought. the difference between million of years and a mere 20.000 of years is not that much 🙂 (not ironic, I work with astronomy on occations)

    Nothing more than heat, well yes, but you have to make the heat useful too. Our old nuclear plant in Barsebäck in southern Sweden (now obsolete) warmed up all the sea of Öregrund so more exotic fishes and other organisms from far south thrived there. I think its efficiency was quite low.

    So how much of the heat generated in a fusion plant can be used to produce electricity? I don't think more than 1%, if I may guess wildly. So the 20.000 year light bulb pehraps dont have to work more than a thousand years after all...

    Thankyou, flexmore, for the information about h-bombs. Now I know why mine never works...
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